Methods for testing for defects on magnetic media storage disks

ABSTRACT

Methods for testing for defects on magnetic media storage disks are provided. One such method includes dividing a surface of a magnetic media disk into a plurality of radial zones, dividing the disk surface into a plurality of concentric zones, thereby forming a preselected number (N) of wedge subsections for each of the concentric zones, scanning the disk surface for defects, counting the defects contained within each of the wedge subsections, summing the defects contained within two or more of the wedge subsections, comparing the summed defects with a preselected threshold, and determining, based on the comparison, a defect type of the disk.

FIELD

The present invention relates generally to processes for testing mediadisks, and more specifically, to methods for testing for defects onmagnetic media storage disks.

BACKGROUND

In the manufacture and assembly of magnetic media storage disks forstorage drives (e.g., hard drives), a number of disk defects arecommonly found. These defects may require debugging that can be bothtime consuming and expensive to perform. A failed disk of this sort willoften have to be removed from a failed drive and subjected to mediacertification or testing to determine if the magnetic disk is usable ornot. The media certification determines the number of defect counts in agiven washer shaped area of the disk. If the number exceeds apredetermined threshold, then the magnetic disk is put aside for furtherprocessing. If the number falls below the predetermined threshold, thenthe magnetic disk is recycled into the hard disk drive manufacturingprocess.

A media test tool such as the MC900 (media certifier 900 series) can beused to perform the media certification. However, a known short-comingof this tool and other such tools in the industry is the ability todetect spiral/circular scratches and light micro scratches. As such, analternative method for detecting and screening out such defects isneeded.

Pattern recognition is an established science that is sometimes appliedto detecting defects on media. Pattern recognition employs complexmathematical modeling to perform feature extraction, feature recognitionand then assimilation of the results for final classification. Whileaspects of pattern recognition are relatively well established, it isbelieved that such techniques have not been successfully applied toaddress the detection of a number of defect types including both lightmicro scratches and spiral/circular scratches.

SUMMARY

Aspects of the invention relate to methods for testing for defects onmagnetic media storage disks. In one embodiment, the invention relatesto a method for testing for defects in magnetic media storage disks, themethod including dividing a surface of a magnetic media disk into aplurality of radial zones, dividing the disk surface into a plurality ofconcentric zones, thereby forming a preselected number (N) of wedgesubsections for each of the concentric zones, scanning the disk surfacefor defects, counting the defects contained within each of the wedgesubsections, summing the defects contained within two or more of thewedge subsections, comparing the summed defects with a preselectedthreshold, and determining, based on the comparison, a defect type ofthe disk.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a process for testing for preselected defectsin magnetic media storage disks in accordance with one embodiment of theinvention.

FIG. 2 is a top schematic view of a media disk divided into wedgesubsections and an algorithm for determining whether type two lightmicro scratch (LMS-2) defects exist in the first four wedge subsectionsof the media disk in accordance with one embodiment of the invention.

FIG. 3 is a flowchart of a process for determining whether type twolight micro scratch (LMS-2) defects exist on a media disk in accordancewith one embodiment of the invention.

FIG. 4 is a top schematic view of a media disk divided into wedgesubsections and an algorithm for determining whether type four lightmicro scratch (LMS-4) defects exist in the first four wedge subsectionsof the media disk in accordance with one embodiment of the invention.

FIG. 5 is a flowchart of a process for determining whether type fourlight micro scratch (LMS-4) defects exist on a media disk in accordancewith one embodiment of the invention.

FIG. 6 is a flowchart of a process for determining whether type sixlight micro scratch (LMS-6) defects exist on a media disk in accordancewith one embodiment of the invention.

FIG. 7 is a flowchart of a process for determining whethermarking/non-uniform type defects exist on a media disk in accordancewith one embodiment of the invention.

FIG. 8 a is a polar plot of light micro scratches on a media disk havingthe scratches roughly concentrated on opposite sides of the disk therebyillustrating two pole or LMS-2 type defects in accordance with oneembodiment of the invention.

FIG. 8 b is a rectangular plot of the light micro scratches on the mediadisk of FIG. 8 a illustrating the two pole or LMS-2 type defects inaccordance with one embodiment of the invention.

FIG. 9 a is a polar plot of light micro scratches on a media disk havingthe scratches roughly concentrated on four areas of the disk therebyillustrating four pole or LMS-4 type defects in accordance with oneembodiment of the invention.

FIG. 9 b is a rectangular plot of the light micro scratches on the mediadisk of FIG. 9 a illustrating the four pole or LMS-4 type defects inaccordance with one embodiment of the invention.

DETAILED DESCRIPTION

The characterization of defects in magnetic media can be important andfairly application specific. With this in mind a discussion of a numberof preselected ways for characterizing defects is believed to behelpful.

FIG. 8 a is a polar plot of light micro scratches on a media disk havingthe scratches roughly concentrated on opposite sides of the disk therebyillustrating two pole or LMS-2 type defects in accordance with oneembodiment of the invention. If the polar plot is extrapolated to arectangular plot, the defects are illustrated as being in two relativelydistinct groups. FIG. 8 b is a rectangular plot of the light microscratches on the media disk of FIG. 8 a illustrating the two pole orLMS-2 type defects in accordance with one embodiment of the invention.

FIG. 9 a is a polar plot of light micro scratches on a media disk havingthe scratches roughly concentrated on four areas of the disk therebyillustrating four pole or LMS-4 type defects in accordance with oneembodiment of the invention. The density or concentration of the defectsdisplayed on the disk illustrate the pattern of four poles that areroughly evenly spaced apart. FIG. 9 b is a rectangular plot of the lightmicro scratches on the media disk of FIG. 9 a illustrating the four poleor LMS-4 type defects in accordance with one embodiment of theinvention.

As can be extrapolated from FIGS. 8 a-9 b, it is also possible to havedefects concentrated in other than two or four groups. In oneembodiment, for example, the light micro scratches are concentrated inroughly six distinct groups to form a six pole or LMS-6 type defect. Inaddition, defects can fall into other categories such as a non-uniformclassification. Defects such as spiral or circular scratches can also befound in conjunction with the defects already discussed.

Referring now to FIGS. 1-7, embodiments of processes for testing forpreselected defects in magnetic media storage disks are illustrated. Theprocesses divide the surface of a magnetic media disk into radial zonesand divide the disk surface into concentric zones, thereby forming apreselected number (N) of wedge subsections for each of the concentriczones. The processes then scan the disk surface for defects whilecounting the defects contained within each wedge subsection. Theprocesses sum the defects contained within two or more of the wedgesubsections and compare the summed defects with preselected thresholds.The processes then determine, based on the comparisons, a defect type ofthe disk. The types of defects can include no defect, a LMS-2 typedefect, a LMS-4 type defect, a LMS-6 type defect, a marking/non-uniformtype defect, a spiral/circular scratch type defect, and/or combinationsof these defect types. Based on the classification of the defect, thedefective disks can be identified quickly and reworked efficiently toaddress the specific defect.

FIG. 1 is a flowchart of a process 100 for testing for preselecteddefects in magnetic media storage disks in accordance with oneembodiment of the invention. The process first divides (102) a surfaceof a magnetic media disk into a plurality of radial zones. In severalembodiments, the radial zones are created by applying one or morediameter lines (e.g., lines extending from one perimeter point of thedisk through the center and to another perimeter point of the disk) to asurface of the disk. In several such embodiments, the radial zones areabout equal in size. In one embodiment, five diameter lines are appliedthereby creating ten radial zones. The process then divides (104) thedisk surface into a plurality of concentric zones, thereby forming apreselected number (N) of wedge subsections for each of the concentriczones. In some embodiments, the process can divide the disk surface intothe concentric zones before dividing the disk surface into radial zones.In one embodiment, the process divides the disk surface into threeconcentric zones and ten radial zones, thereby forming 30 wedgesubsections.

The process then scans (106) the disk surface for defects. In oneembodiment, the process performs one or more tone scans and/or othersuitable scans known in the art. The process counts (108) the defectscontained within each of the wedge subsections. The process then sums(110) the defects contained within two or more of the wedge subsections.In several embodiments, the wedge subsections that are summed vary inaccordance with the type of defect to be detected. The process compares(112) the summed defects with one or more preselected thresholds. In anumber of embodiments, the preselected thresholds are determined basedon the results of empirical testing. The process then determines (114),based on the comparison, a defect type of the disk. In some cases theremay be no defect. In other cases, the defect types can include a LMS-2type defect, a LMS-4 type defect, a LMS-6 type defect, amarking/non-uniform type defect, a spiral/circular scratch type defect,and/or combinations of these or other known defect types. Based on theclassification of the defect, the defective disks can be identifiedquickly and reworked efficiently to address the specific defect.

In one embodiment, the process can perform the sequence of actions in adifferent order. In another embodiment, the process can skip one or moreof the actions. In other embodiments, one or more of the actions areperformed simultaneously. In some embodiments, additional actions can beperformed.

FIG. 2 is a top schematic view of a media disk 200 divided into wedgesubsections (W1-W30) and an algorithm (202-206) for determining whethertype two light micro scratch (LMS-2) defects exist in the first fourwedge subsections (W1-W4) of the media disk in accordance with oneembodiment of the invention. As can be seen in FIG. 2, the disk surfacehas been divided into three concentric zones and ten radial zones,thereby forming the 30 wedge subsections (W1-W30). In other embodiments,the disk surface can be divided into more than or less than threeconcentric zones, and more than or less than ten radial zones. Inseveral embodiments, the disk surface includes a number of media tracks.In one such embodiment, the inner concentric zone includes about 30percent of the media tracks, the middle concentric zone includes about50 percent of the media tracks, and the outer concentric zone includesabout 20 percent of the media tracks. In other embodiments, the zonescan be arranged to provide for other suitable percentages of the mediatracks.

The algorithm first sums (202) the defects found in the first two wedgesections (W1, W2) and determines whether the sum is greater than 5,000.The algorithm then sums (204) the defects found in the second two wedgesections (W3, W4) and determines whether the sum is less than 1,000. Thealgorithm then determines (206) whether both such conditions are true,and, if so, stores information indicative of a LMS-2 type defect havingbeen found on the disk. In the algorithm, preselected defect thresholdsof 1,000 and 5,000 are used. In other embodiments, other suitablethresholds can be used.

FIG. 3 is a flowchart of a process 300 for determining whether type twolight micro scratch (LMS-2) defects exist on a media disk in accordancewith one embodiment of the invention. In particular embodiments, process300 can be used with the media disk of FIG. 2 and/or in conjunction withthe process of FIG. 1. The process 300 first divides (302) the disksurface into N wedge subsections and sets an index variable I to beequal to 1. In some embodiments, the disk surface may be divided inaccordance with steps 102 and 104 of the process 100 of FIG. 1. In oneembodiment, N is 30.

The process then determines (304) whether the expression “Sum[W(I),W(I+1)]>5,000 AND Sum[W(I+2), W(I+3)]<1000” is true. The former being acomparison of the sum of defects for wedge subsections W(I) and W(I+1)and a first preselected defect threshold of 5,000. The latter being acomparison of the sum of defects for wedge subsections W(I+2) and W(I+3)and a second preselected defect threshold of 1,000. If the expression istrue, then the process has detected (306) a LMS-2 type defect. If theexpression is false, then the process determines (308) whether all ofthe wedge subsections have been counted by examining the expression“I+3=N”. If all of the wedge subsections have been counted, then theprocess notes (310) that no LMS-2 type defects were found. If all of thewedge subsections have not been counted, the process increments (312)the index variable I and returns to determining (304) the sum expressionfor the next group of wedge subsections.

In one embodiment, the process can perform the sequence of actions in adifferent order. In another embodiment, the process can skip one or moreof the actions. In other embodiments, one or more of the actions areperformed simultaneously. In some embodiments, additional actions can beperformed.

FIG. 4 is a top schematic view of a media disk 400 divided into wedgesubsections (W1-W30) and an algorithm (402-406) for determining whethertype four light micro scratch (LMS-4) defects exist in the first fourwedge subsections (W1-W4) of the media disk in accordance with oneembodiment of the invention. As can be seen in FIG. 4, the disk surfacehas been divided into three concentric zones and ten radial zones,thereby forming the 30 wedge subsections (W1-W30). In other embodiments,the disk surface can be divided into more than or less than threeconcentric zones, and more than or less than ten radial zones. Thealgorithm first sums (402) the defects found in the first two odd wedgesubsections (W1, W3) and determines whether the sum is less than 1,000.The algorithm then sums (404) the defects found in the first two evenwedge subsections (W2, W4) and determines whether the sum is greaterthan 5,000. The algorithm then determines (406) whether both suchconditions are true, and, if so, stores information indicative of aLMS-4 type defect having been found on the disk. In the algorithm,preselected defect thresholds of 1,000 and 5,000 are used. In otherembodiments, other suitable thresholds can be used.

FIG. 5 is a flowchart of a process 500 for determining whether type fourlight micro scratch (LMS-4) defects exist on a media disk in accordancewith one embodiment of the invention. In particular embodiments, process500 can be used in conjunction with the media disk of FIG. 4 and/or theprocesses of FIGS. 1 and 3. Process 500 continues from block 310 ofprocess 300 where it was determined that no LMS-2 type defects werefound and sets an index variable I to be equal to 1 in block 502.

The process then determines (504) whether the expression “Sum[W(I),W(I+2)]>5,000 AND Sum[W(I+1), W(I+3)]<1000” is true. The former being acomparison of the sum of defects for wedge subsections W(I) and W(I+2)and a first preselected defect threshold of 5,000. The latter being acomparison of the sum of defects for wedge subsections W(I+1) and W(I+3)and a second preselected defect threshold of 1,000. If the expression istrue, then the process has detected (506) a LMS-4 type defect. If theexpression is false, then the process determines (508) whether all ofthe wedge subsections have been counted by examining the expression“I+3=N”. If all of the wedge subsections have been counted, then theprocess notes (510) that no LMS-4 type defects were found. If all of thewedge subsections have not been counted, the process increments (512)the index variable I and returns to determining (504) the sum expressionfor the next group of wedge subsections.

In one embodiment, the process can perform the sequence of actions in adifferent order. In another embodiment, the process can skip one or moreof the actions. In other embodiments, one or more of the actions areperformed simultaneously. In some embodiments, additional actions can beperformed.

FIG. 6 is a flowchart of a process 600 for determining whether type sixlight micro scratch (LMS-6) defects exist on a media disk in accordancewith one embodiment of the invention. In particular embodiments, process600 can be used in conjunction with the media disk of FIG. 4 and/or theprocesses of FIGS. 1, 3 and 5. Process 600 continues from block 510 ofprocess 500 where it was determined that no LMS-2 and no LMS-4 typedefects were found and sets an index variable I to be equal to 1 inblock 602.

The process then determines (604) whether the expression “Sum[W(I),W(I+2)]>5,000 AND Sum[W(I+1), W(I+3)]<3000” is true. The former being acomparison of the sum of defects for wedge subsections W(I) and W(I+2)and a first preselected defect threshold of 5,000. The latter being acomparison of the sum of defects for wedge subsections W(I+1) and W(I+3)and a second preselected defect threshold of 3,000. If the expression istrue, then the process has detected (606) a LMS-6 type defect. If theexpression is false, then the process determines (608) whether all ofthe wedge subsections have been counted by examining the expression“I+3=N”. If all of the wedge subsections have been counted, then theprocess notes (610) that no LMS-6 type defects were found. If all of thewedge subsections have not been counted, the process increments (612)the index variable I and returns to determining (604) the sum expressionfor the next group of wedge subsections.

In one embodiment, the process can perform the sequence of actions in adifferent order. In another embodiment, the process can skip one or moreof the actions. In other embodiments, one or more of the actions areperformed simultaneously. In some embodiments, additional actions can beperformed.

FIG. 7 is a flowchart of a process 700 for determining whethermarking/non-uniform type defects exist on a media disk in accordancewith one embodiment of the invention. In particular embodiments, process700 can be used in conjunction with the media disk of FIG. 4 and/or anythe processes discussed above. Process 700 continues from block 610 ofprocess 600 where it was determined that no LMS-2, LMS-4, or LMS-6 typedefects were found and sets an index variable I to be equal to 1 inblock 702.

The process then determines (704) whether the expression “Sum[W(I),W(I+1)]>5,000 AND Sum[W(I+2), W(I+3), . . . ,W(N)]<3000” is true. Theformer being a comparison of the sum of defects for wedge subsectionsW(I) and W(I+1) and a first preselected defect threshold of 5,000. Thelatter being a comparison of the sum of defects for all wedgesubsections except the first two and a second preselected defectthreshold of 3,000. If the expression is true, then the process hasdetected (706) a marking/non-uniform type defect. If the expression isfalse, then the process notes (708) that no LMS-6 type defects werefound.

In another embodiment, the process 700 can continue in order to detectwhether a spiral or circular type defect exists. In such case, theprocess 700 would continue from block 708 where it was determined thatno LMS-2, LMS-4, LMS-6, or marking type defects were found and determinewhether a new sum expression of“Sum[W(1),W(2),W(3),W(4),W(5),W(6)]>3,000 ORSum[W(3),W(4),W(5),W(6),W(7),W(8)]>3,000 OR Sum[W(5),W(6),W(7),W(8),W(9)]>3,000” is true. If the new sum expression is true, then theprocess has detected a spiral or circular type defect (e.g., ringdefect). If the expression is false, then the process notes that nospiral/circular type defects were found.

In one embodiment, the process can perform the sequence of actions in adifferent order. In another embodiment, the process can skip one or moreof the actions. In other embodiments, one or more of the actions areperformed simultaneously. In some embodiments, additional actions can beperformed.

While the above description contains many specific embodiments of theinvention, these should not be construed as limitations on the scope ofthe invention, but rather as examples of specific embodiments thereof.Accordingly, the scope of the invention should be determined not by theembodiments illustrated, but by the appended claims and theirequivalents.

What is claimed is:
 1. A method for testing for defects in magneticmedia storage disks, the method comprising: dividing a surface of amagnetic media disk into a plurality of radial zones; dividing the disksurface into a plurality of concentric zones, thereby forming apreselected number (N) of wedge subsections for each of the concentriczones; scanning the disk surface for defects; counting the defectscontained within each of the wedge subsections; summing the defectscontained within two or more of the wedge subsections; comparing thesummed defects with a preselected threshold; and determining, based onthe comparison, a defect type of the disk.
 2. The method of claim 1,wherein the defect type is selected from the group consisting of anon-defect type, a first defect type, a second defect type, a thirddefect type, and a fourth defect type.
 3. The method of claim 2: whereinthe first defect type comprises a LMS-2 defect type, wherein the seconddefect type comprises a LMS-4 defect type, wherein the third defect typecomprises a LMS-6 defect type, and wherein the fourth defect typecomprises a non-uniform defect type.
 4. The method of claim 1, whereinthe summing the defects contained within the two or more wedgesubsections comprises: calculating a sum of the defects in wedgesubsection (I) and wedge subsection (I+X), wherein X is a numberselected from the group consisting of 1, 2 and 3, and I is a positiveinteger that ranges from 1 to N.
 5. The method of claim 1, wherein thesumming the defects contained within the two or more wedge subsectionscomprises: (4a) calculating a first sum of the defects in a wedgesubsection (I) and a wedge subsection (I+1); (4b) calculating a secondsum of the defects in a wedge subsection (I+2) and a wedge subsection(I+3), wherein I is a positive integer that ranges from 1 to N; (4c)determining whether the first sum is greater than a preselected firstsum threshold; (4d) determining whether the second sum is less than apreselected second sum threshold; (4e) classifying, if both conditions(4c) and (4d) are true, the disk as having a first defect type;repeating, if either condition (4c) is not true or condition (4d) is nottrue, steps (4a) through (4e) after incrementing I by
 1. 6. The methodof claim 5, wherein the summing the defects contained within the two ormore wedge subsections further comprises: if the disk does not have thefirst defect type: (5a) calculating a third sum of the defects in awedge subsection (I) and a wedge subsection (I+2); (5b) calculating afourth sum of the defects in a wedge subsection (I+1) and a wedgesubsection (I+3); (5c) determining whether the third sum is greater thana preselected third sum threshold; (5d) determining whether the fourthsum is less than a preselected fourth sum threshold; (5e) classifying,if both conditions (5c) and (5d) are true, the disk as having a seconddefect type; repeating, if either condition (5c) is not true orcondition (5d) is not true, steps (5a) through (5e) after incrementing Iby
 1. 7. The method of claim 6, wherein the summing the defectscontained within the two or more wedge subsections further comprises: ifthe disk does not have the first defect type and the disk does not havethe second defect type: (6a) calculating a fifth sum of the defects in awedge subsection (I) and a wedge subsection (I+2); (6b) calculating asixth sum of the defects in a wedge subsection (I+1) and a wedgesubsection (I+3); (6c) determining whether the fifth sum is greater thana preselected third sum threshold; (6d) determining whether the sixthsum is less than a preselected fifth sum threshold; (6e) classifying, ifboth conditions (6c) and (6d) are true, the disk as having a thirddefect type; repeating, if either condition (6c) is not true orcondition (6d) is not true, steps (6a) through (6e) after incrementing Iby
 1. 8. The method of claim 7, wherein the summing the defectscontained within the two or more wedge subsections further comprises: ifthe disk does not have the first defect type and the disk does not havethe second defect type and the disk does not have the third defect type:(6a) calculating a seventh sum of the defects in a wedge subsection (I)and a wedge subsection (I+1); (6b) calculating an eighth sum of thedefects in all of the wedge subsections of a selected concentric zoneexcept the wedge subsection (I) and the wedge subsection (I+1); (6c)determining whether the seventh sum is greater than a preselectedseventh sum threshold; (6d) determining whether the eighth sum is lessthan a preselected eighth sum threshold; (6e) classifying, if bothconditions (6c) and (6d) are true, the disk as having a fourth defecttype; repeating, if either condition (6c) is not true or condition (6d)is not true, steps (6a) through (6e) after incrementing I by
 1. 9. Themethod of claim 1, wherein N is about equal to
 30. 10. The method ofclaim 1, wherein the concentric zones comprise three concentric zones.11. The method of claim 10: wherein the disk surface comprises aplurality of tracks, and wherein the three concentric zones comprise: afirst concentric zone covering about 20 percent of the tracks; a secondconcentric zone covering about 50 percent of the tracks; and a thirdconcentric zone covering about 30 percent of the tracks.
 12. The methodof claim 1, wherein the scanning the disk surface for the defectscomprises performing tone scanning on the disk surface.
 13. The methodof claim 1, wherein the dividing the surface of the magnetic media diskinto radial zones comprises dividing the surface of the magnetic mediadisk into radial zones that have about equal size.